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Can you build a key charger?

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Dablk
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Can you build a key charger?

Post by Dablk » Wed Aug 16, 2017 4:42 pm

For most of us our Z4m are more of occasional cars than daily's

So with two keys I'm unlikely to regular get the 30hrs of recommended full charge time in. I'm definitely not going to leave them in the car overnight as I have seen suggested. I don't have a problem yet but also want to try and avoid one.

So started to think if it would be possible to send a signal to a spare induction ring and charge them in the house?

Any electrical savvy folks on here?

Is it just a case of sending a 12v feed to the ring or more complicated than this?

Any chance you could wipe your key doing it? I would have though the ring is just a standard bit of kit and its the control module (which wont be attached that does any damage.

Any thoughts?

Chris
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markplant
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Can you build a key charger?

Post by markplant » Wed Aug 16, 2017 4:47 pm

Am sure some have used tooth brush charges, it works on induction, like the new phones that do wireless charging
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Dablk
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Can you build a key charger?

Post by Dablk » Wed Aug 16, 2017 4:52 pm

Yeah agreed on that part. Its the black ring around the ignition barrel which does the work. its how it works I'm looking for guidance on if anyone knows.
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exdos
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Can you build a key charger?

Post by exdos » Wed Aug 16, 2017 4:55 pm

I use an electric tooth brush charging base unit which works.

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GuidoK
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Can you build a key charger?

Post by GuidoK » Wed Aug 16, 2017 4:57 pm

Dablk wrote: Wed Aug 16, 2017 4:42 pm
Is it just a case of sending a 12v feed to the ring or more complicated than this?
It cant be a 12v DC feed to the ring unless it has some kind of DC-AC converter in it.
It HAS to be an alternating electromagnetic field to work.

And it could be that it has to have a specific frequency, depending on the scematic.
The coil is directly fed from the EWS, so not directly from the battery
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Dablk
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Can you build a key charger?

Post by Dablk » Wed Aug 16, 2017 7:19 pm

Cheers folks,
Yes I know of the toothbrush trick. Was just trying to create a mini project.

Not massively electric savvy. I know the ring has stamped on 125khz And only has a two pin connection.
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Can you build a key charger?

Post by GuidoK » Wed Aug 16, 2017 7:37 pm

Dablk wrote: Wed Aug 16, 2017 7:19 pm
Not massively electric savvy. I know the ring has stamped on 125mhz. And only has a two pin connection.
Afaik the coil serves both as an antenna for the key's transponder and as wireless charging for the key's battery.
I'm pretty sure the 125mhz isnt the charging frequency but rather the transponders' frequency :)
So its fed with a duplex signal in the car.

You could make your own ring antenna and hook it up to a scope to see the frequency :)
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Dablk
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Can you build a key charger?

Post by Dablk » Wed Aug 16, 2017 8:29 pm

Cheers,
Got an old toothbrush charger and a key set from an e46. Going to cut some stuff up for a laugh. As said sometimes just like a side project to mess around with.

Will see if I can build somthing and see a voltage signal on the e46 key.
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Can you build a key charger?

Post by Taz » Wed Aug 16, 2017 8:44 pm

I was wonder how you know your key as been charged

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exdos
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Can you build a key charger?

Post by exdos » Wed Aug 16, 2017 8:47 pm

Taz wrote: Wed Aug 16, 2017 8:44 pm I was wonder how you know your key as been charged
If it doesn't work before it goes onto the charger and then it does work after several hours on the charger, that convinces me. :thumbsup:

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Can you build a key charger?

Post by enzed4 » Wed Aug 16, 2017 8:49 pm

Taz wrote: Wed Aug 16, 2017 8:44 pm I was wonder how you know your key as been charged
^^ This ^^

How will you know your project (or any method of charging) is successful, other than knowing its failed if the key battery goes flat?
Anyone know if a Qi wireless charger for a phone would work (I think they are 5v/1000mAh, so if the key needs 12V, I guess not)?

Edit - quick google search shows that the Qi chargers don't work with the key fobs
Last edited by enzed4 on Wed Aug 16, 2017 9:22 pm, edited 1 time in total.
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Taz
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Can you build a key charger?

Post by Taz » Wed Aug 16, 2017 8:49 pm

Lol

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Dablk
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Can you build a key charger?

Post by Dablk » Wed Aug 16, 2017 8:51 pm

Cut test key in half.. measure battery voltage. if it goes up. It's charging off the project.
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Can you build a key charger?

Post by exdos » Wed Aug 16, 2017 8:53 pm

Dablk wrote: Wed Aug 16, 2017 8:51 pm Cut test key in half.. measure battery voltage. if it goes up. It's charging off the project.
Have you seen the price of these keys?

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Dablk
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Can you build a key charger?

Post by Dablk » Wed Aug 16, 2017 9:03 pm

I might be mad but not mental enough to cut a new one in half.
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| 07 Carbon Z4MC | Black Nappa | Carbon Leather |
| Oem 224 or CS Wheels In Anthracite | Loads of Toys | Iso Fix for Little One Days Out |
| 37K - June 17 |

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